OFFSET
0,5
REFERENCES
S. Giraudo, Algebraic and combinatorial structures on pairs of twin binary trees, Journal of Algebra, Volume 360, 15 June 2012, Pages 115-157.
LINKS
S. Giraudo, Algebraic and combinatorial structures on Baxter permutations, DMTCS proc. AO, FPSAC 2011 Rykjavik, (2011) 387-398.
FORMULA
Giraudo gives a generating function.
PROG
(PARI)
baxter(n) = sum(k=1, n, binomial(n+1, k-1) * binomial(n+1, k) * binomial(n+1, k+1) / (binomial(n+1, 1) * binomial(n+1, 2)));
lista(m) = {u = t + t*O(t^m); b = 1 + sum(n=1, m, baxter(n)*u^n); gfbt = (b-1)/b^2; for (n=0, m, print1(polcoeff(gfbt, n, t), ", ")); }
\\ Michel Marcus, Feb 16 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 03 2012
EXTENSIONS
More terms from Michel Marcus, Feb 16 2013
STATUS
approved